A LENS IS TESTING ME

[Robert Hart]

I have a Sigma 50m-500 f4-f6.3 zoom. Over the years the image has become a bit spotty. The nature of the design is that in dusty conditions encountered when chasing aeroplanes in ground-to-air shots, it is inevitable that the lens will hoover up dust as the zoom extension goes in and out. This one has also hoovered up some fungus spores and it is now rampant inside.

The cost of getting it torn down and cleaned is likely more than the cost of buying a used good one off eBay. Lens repairers may also not be too keen on infecting their shop with fungus. I have successfully defungussed Cooke Panchros and Angenieux zooms but this one is going to be a mission. The fungus is on the travelling optical groups deep inside as well as the front element, which is an easy fix.

I cannot find any service literature on the web for this lens. As close as I can get is an exploded view for a 100-400 zoom but there are some differences.

I am putting this query out there in the hope that someone may have a service manual or exploded view of the parts of this lens or even a correct order of dissembly/reassembly. Here's hoping because one can get into a dreadful mess just mining in blindly.


Cheers.

 

[Robert Hart]

After a few tormentous days, I got the lens fixed in time for an aviation event tomorrow. However any diagrams or service info on this lens will remain appreciated as I have work to do on it yet.

 

[Robert Hart]

Here is a bit of vision from the day with the repaired lens. The follows could have been better. I had crook eyes from ryegrass allergy and had taken mediciation which messes with one's reaction times..